1. Field of the Invention
This invention relates to a centrifuge including a rotor in which a sample (or samples) to be analyzed is placed, and a drive device for rotating the rotor to separate the sample according to centrifugal force.
2. Description of the Related Art
A general centrifuge or a general centrifugal separator includes a rotor in which a sample (or samples) to be analyzed is placed. A motor-based drive device rotates the rotor at a high speed. The rotor is connected with the drive device via a vertically-extending rotary shaft.
The rotary shaft is designed to be flexible and thin to reduce a bearing load caused by an imbalance in the rotor or an imbalance in the sample arrangement during high-speed rotation of the rotor. Therefore, the spring modulus of the rotary shaft is relatively low.
The drive device is connected with a centrifuge support frame via viscoelastic members. The viscoelastic members have both the spring function and the damping function. For example, the viscoelastic members include suitable combinations of rubber vibration isolators, helical springs, and dampers.
In general, a portion of the body of the centrifuge resonates when the rotor is rotated at one of specified speeds (resonant speeds). The damping function of the viscoelastic members is effective in reducing the amplitude of resonance vibration of the centrifuge body portion which would be increased by an imbalance in the rotor or an imbalance in the sample arrangement.
In the case where the viscoelastic members have a relatively high spring modulus, they hardly deform and hence the damping function thereof tends to be ineffective during rotation of the rotor at a resonant speed. On the other hand, the rotary shaft is whirled or bent considerably out of true through the effect of centrifugal force since the spring modulus thereof is relatively low. Such a bend tends to cause plastic deformation of the rotary shaft or unwanted contact between the outer surface of the rotor and the inner surface of a rotor casing. Accordingly, the viscoelastic members are generally designed to have a relatively low spring modulus. In this case, when the weight of the rotor is great, the viscoelastic members tend to be excessively expanded and be damaged.
It is an object of this invention to provide an improved centrifuge.
A first aspect of this invention provides a centrifuge comprising a rotor; a drive device for rotating the rotor; a support frame located between the rotor and the drive device; a viscoelastic member provided between the support frame and the drive device; and means for locating the drive device in an axial direction.
A second aspect of this invention is based on the first aspect thereof, and provides a centrifuge wherein the locating means comprises a suspension connecting the support frame and a bottom of the drive device, and the suspension includes one of a wire rope and a piano wire.
A third aspect of this invention is based on the first aspect thereof, and provides a centrifuge further comprising a rotary shaft connected between the rotor and the drive device, wherein a sum of a spring modulus of the viscoelastic member and a spring modulus of the suspension is smaller than a spring modulus of the rotary shaft.
A fourth aspect of this invention is based on the first aspect thereof, and provides a centrifuge wherein the viscoelastic member has a rubber hardness of 35xc2x0 or less.
A fifth aspect of this invention is based on the first aspect thereof, and provides a centrifuge wherein the suspension has an end including an adjuster for varying a length of the suspension.
A sixth aspect of this invention provides a centrifuge comprising a rotor; a drive device for rotating the rotor; a support frame located between the rotor and the drive device; a viscoelastic member provided between the support frame and the drive device; and a suspension provided between the support frame and the drive device.
A seventh aspect of this invention is based on the sixth aspect thereof, and provides a centrifuge wherein the suspension comprises a wire provided between the support frame and the drive device.
An eighth aspect of this invention is based on the sixth aspect thereof, and provides a centrifuge wherein the suspension comprises an adjuster for varying a length of the suspension.
A ninth aspect of this invention is based on the sixth aspect thereof, and provides a centrifuge further comprising a vertically-extending rotary shaft connected between the rotor and the drive device, wherein a sum of a spring modulus of the viscoelastic member and a spring modulus of the suspension is smaller than a spring modulus of the rotary shaft in a horizontal direction.